A crankshaft is mechanical equipment that transforms the reciprocating movement of the piston into rotary motion. A crankshaft connects with the piston through a connecting rod. The main objective of this connecting rod is to receive reciprocating motion from the piston and delivers it to the crankshaft.
An engine crankshaft runs inside the bottom end of a car’s motor and converts the vertical movement of the pistons into horizontal rotational movement, which ultimately drives the wheels via the gearbox. The crankshaft is attached to the engine by large bearings at either end. It connects to the flywheel, and through that, the clutch.
When the clutch is engaged, the rotational energy of the crankshaft is transmitted through the gearbox and on through the differential to the driveshafts, which are attached to the wheels, hence creating the car’s ability to move.
A crankshaft works on the crank mechanism. A crank has crankpins and cranks which are connected with the connecting rods. It has a vibration damper that reduces the thrust on the crank.
How does the crankshaft work?
The crank has a counterweight which use to decrease the bending load on the crank. A crankshaft of a 4-stroke engine works in the following way:
- As the engine piston moves from TDC to BDC, it transfer its motion to the crankshaft via a connecting rod.
- The crank further transforms the piston’s linear motion into rotary motion and transfer it to the camshaft.
- As the camshaft receives rotary motion, it opens the inlet valve, and the air-fuel mixture enters into the combustion chamber.
- As the combustion chamber is filled with the air-fuel mixture, the piston moves upward and compresses the mixture. During this process, the camshaft closes both inlet and exhaust valves. As the compression process completes, the first revolution of the crankshaft also completes.
- At the end of the compression process, the ignition process takes place.
- The heat released by the compressed mixture due to the ignition process forces the piston to move downward. This stroke is known as a power stroke. During this piston’s downward, the piston again transfers its reciprocating to connecting rod, which further sends it to the crankshaft.
- On end of the crank connects with the flywheel. As the crank receives the piston’s motion, it transfers this motion to the flywheel. The flywheel stores this motion and further drives the vehicle wheels.
- After power stroke, the piston further moves downward for discharging the exhaust gases. During this process, the camshaft receives the piston’s motion by the crank and opens the exhaust valve while the inlet valve remains closed. The piston pushes the exhaust gases out of the combustion chamber.
Function of the crankshaft
The crankshaft converts the force generated by the combustion in the engine into rotary motion. The linear upwards and downwards motion of the pistons is converted into a torque by the connecting rod and then transmitted to the fly wheel.
Construction and properties
To withstand the heavy loads involved, crankshafts have a hardened surface and a tough core. Therefore, crankshafts are often made of forged steel. The continuous grain course enables a high torsion resistance to be achieved. The bearing positions on the crankshaft are surface hardened, making them more resistant to wear.
Crankshafts can generally be forged from casts in ductile steels or by roll forging by using steel bars. Nowadays, maximum manufactures use forged crankshafts because of their excellent inherent damping, compact design, and lightweight.
Vanadium micro-alloyed steel mainly uses for the forged crankshaft. This is because these steels can be air-cooled without further heat treatment except the bearing surface hardening once they have reached a high strength. It also has a lower alloy content which makes the material low-cost as compared to high alloy steel.
Nowadays, only some engines use crankshafts of the cast iron for the cheap and low-power version, while the more costly and high-power versions of engines use forged steel crankshafts.
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